The present invention relates to a plane carbon commutator to be used as a commutator for a motor of a fuel pump or the like, for example, and its manufacturing method, and relates more particularly to a plane carbon commutator and its manufacturing method for ensuring a coupling between a segment and a carbon in a commutator.
A plane carbon commutator has such a structure in which a metal segment is fixed to an end surface of a commutator main body made of a mold resin and a carbon is fixed to this segment. As methods for manufacturing a plane carbon commutator of this type, there are following methods (A) to (D), for example.
(A) When a carbon is molded, a metal base material which becomes a segment is inserted into the carbon for integrating these together and these are burned. Then, the metal base material integrally molded with carbon is molded with a mold resin to form an insulating material section. (For example, see Japanese Patent Application Laid-Open No. 95-264812) PA1 (B) An insulating material and a metal base material are integrated together by an integral molding in advance, and thereafter carbon is adhered on the surface of the metal base material with solder or with conductive adhesive agent. (For example, see International Publication No. WO93/01321) PA1 (C) An insulating material and a metal base material are integrated together by an integral molding in advance, and thereafter carbon is formed on the surface of the metal base material and burned. (For example, see Japanese Utility Model Application Publication No. 951 42223) PA1 (D) An insulating material and a metal base material are separately prepared in advance, and the insulating material and the metal base material are inserted into carbon for integrally molding these together at the time of molding the carbon. (For example, see Japanese Patent Application Laid-Open No. 94-178503)
According to the above-described method (A), the temperature for burning the carbon is as high as at least about 600.degree. C., so that there is a problem that the metal base material to be integrally molded is softened and this generates difficulties in the product precision and strength improvement. To avoid this problem, it is possible to burn the carbon at a low temperature of about 200.degree. C. However, in this case, the material quality of the carbon itself becomes special with a resultant problem in various characteristics such as hardness, electric resistivity, gasoline-proof, etc.
According to the above-described method (B), the carbon can be burned as a single in advance and there is no quality problem of the carbon itself. However, in the structure of having the carbon soldered on the surface of the metal base material, there is a risk of an occurrence of a loosening of the solder due to the high temperature at the time of connection fusing for assembling the motor.
Further, in the structure of having the metal base material and the carbon adhered together by using a conductive adhesive agent, an adhesive agent having both conductivity and gasoline-proof is necessary, which results in an expensive structure. Further, even if the adhesive agent has conductivity, the electric resistance becomes larger than that of the carbon and the metal base material, holding a problem that this portion has the risk of heat generation and quality change during the operation of the motor.
According to the above-described method (C), the insulating material made of resin is carbonized at a high temperature when the carbon is burned on the surface of the metal base material, so that the carbon must be burned at a low temperature, which results in a quality problem of the carbon.
The above-described method (D) has a problem similar to that in the above-described method (C).